1. Field of the Invention
The invention relates to dry accelerometers of the pendulous mass type used in inertial navigation systems. More particularly, this invention pertains to an integrated accelerometer assembly.
2. Description of the Prior Art
Dry closed loop accelerometers of the hinged, pendulous mass type have substantially replaced floated accelerometers in modern strapdown inertial navigation systems due to the smaller volume, lighter weight and simplified construction that they offer. Functionally, a common type of single-axis dry accelerometer comprises a pendulous mass that is suspended within a housing by flexure type hinges. When subjected to acceleration, the mass pivots or rotates about the hinge axis to thereby shutter the output of a light emitting diode conventionally located adjacent the mass' non-pivotal or free end. This is detected by a photodetector circuit. The photodetector circuit produces an output signal that is proportional to the sensed acceleration. Such signal is amplified and the resultant current is applied to a torquer coil that is mounted to the pendulous mass. The coil reacts with a permanent magnet that is affixed to the housing to return the mass to a substantially neutral (null) position. The torquing current thereby provides a measure of the input acceleration.
While the foregoing arrangement of a dry accelerometer may provide excellent performance in a relatively small package, its manufacture requires intensive manual assembly and adjustment resulting in substantial cost. The conventional design includes minute components which are attached by Epoxy or solder in processes that require highly dextrous and skilled personnel. The Epoxy bonds that attach the pendulous mass to the housing tend to "creep" over time, resulting in critical misalignment that can effectively limit the instrument's life as it can acquire undesirable sensitivity to off-axis accelerations.